Mercurial_ The Definitive Guide - Bryan O'Sullivan [10]
The core of Git is written in C. Many Git commands are implemented as shell or Perl scripts, and the quality of these scripts varies widely. I have encountered several instances where scripts charged along blindly in the presence of errors that should have been fatal.
Mercurial can import revision history from a Git repository.
CVS
CVS is probably the most widely used revision control tool in the world. Due to its age and internal untidiness, it has been only lightly maintained for many years.
It has a centralized client/server architecture. It does not group related file changes into atomic commits, making it easy for people to “break the build”: one person can successfully commit part of a change and then be blocked by the need for a merge, causing other people to see only a portion of the work they intended to do. This also affects how you work with project history. If you want to see all of the modifications someone made as part of a task, you will need to manually inspect the descriptions and timestamps of the changes made to each file involved (if you even know what those files were).
CVS has a muddled notion of tags and branches that I will not attempt to even describe. It does not support renaming of files or directories well, making it easy to corrupt a repository. It has almost no internal consistency checking capabilities, so it is usually not even possible to tell whether or how a repository is corrupt. I would not recommend CVS for any project, existing or new.
Mercurial can import CVS revision history. However, there are a few caveats that apply; these are true of every other revision control tool’s CVS importer, too. Due to CVS’s lack of atomic changes and unversioned filesystem hierarchy, it is not possible to reconstruct CVS history completely accurately; some guesswork is involved, and renames will usually not show up. Because a lot of advanced CVS administration has to be done by hand and is hence error-prone, it’s common for CVS importers to run into multiple problems with corrupted repositories (completely bogus revision timestamps and files that have remained locked for over a decade are just two of the less interesting problems I can recall from personal experience).
Mercurial can import revision history from a CVS repository.
Commercial Tools
Perforce has a centralized client/server architecture, with no client-side caching of any data. Unlike modern revision control tools, Perforce requires that a user run a command to inform the server about every file they intend to edit.
The performance of Perforce is quite good for small teams, but it falls off rapidly as the number of users grows beyond a few dozen. Modestly large Perforce installations require the deployment of proxies to cope with the load their users generate.
Choosing a Revision Control Tool
With the exception of CVS, all of the tools listed above have unique strengths that suit them to particular styles of work. There is no single revision control tool that is best in all situations.
As an example, Subversion is a good choice for working with frequently edited binary files, due to its centralized nature and support for file locking.
I personally find Mercurial’s properties of simplicity, performance, and good merge support to be a compelling combination that has served me well for several years.
Switching from Another Tool to Mercurial
Mercurial is bundled with an extension named convert, which can incrementally import revision history from several other revision control tools. By “incremental,